Thanks for the advice Kev. I have a metal mule pipe with 2into1 (dirt bike type) headers on a different bike. I can see here the flow would be more uninterupted than a H design.

On the bike I'm working on now, If I ran the standard design headers but delete the H pipe under the engine, would the Y form under the engine for a couple of inches then branch out into two (around the bash plate mount)? only problem I can see here is a lack of room.

It may be better to design a pipe more like the (dirt bike) 2into1 and run 1 big pipe. Only problem here is the shops here dont mandrel bend. They cut and TIG weld preformed bends. I had a single T4 muffler on a KLR650. sounded mean as anything. quite loud but I liked it, so it would be pretty much the same sound on the 660.
[IMG] [/IMG]

Having the 2into1 Y would be an advantage as it would form so much easier under the engine, then just run off to one side. I think it would be less technical for the locals to build rather than a dirt bike styled 2into1.

I'm setting the bikes up for tours here in Asia so the single pipe option would be better as I could then run a solid side case on the opposite side for storage.

Im still trying to decide the best way to go so any input would be good.
Just one other question Kev, can I delete the O2 sensor (maybe with the addition of an o2 eliminator) or is it a crucial part on the 2010 model?
thanks Kev...